USACE / NAVFAC / AFCESA / NASA UFGS-31 05 21 (August 2008)
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Preparing Activity: USACE Superseding
UFGS-31 05 21 (April 2006)
UNIFIED FACILITIES GUIDE SPECIFICATIONS
References are in agreement with UMRL dated January 2009
SECTION 31 05 21
GEOGRID SOIL REINFORCEMENT
08/08
NOTE: This guide specification covers the requirements for geogrid reinforcement
to enhance the veneer soil stability for landfill liners and covers.
Edit this guide specification for project specific requirements by adding, deleting,
or revising text. For bracketed items, choose applicable items(s) or insert
appropriate information.
Remove information and requirements not required in respective project, whether
or not brackets are present.
Comments and suggestions on this guide specification are welcome and should
be directed to the technical proponent of the specification. A listing of technical
proponents, including their organization designation and telephone number, is
on the Internet.
Recommended changes to a UFGS should be submitted as a Criteria Change Request
(CCR).
PART 1 GENERAL
NOTE: Geometric requirements such as slope length, and construction limits
should be shown on the drawings.
1.1 MEASUREMENT AND PAYMENT
The unit of measurement for soil slope reinforcement will be square meters (SM) yards (SY). Overlaps for splices
(if allowed) and for the Contractor's convenience will not be measured for payment. Payment will be made at
the respective unit price listed on the bidding schedule. Payment will be full compensation for furnishing all
material, labor, equipment, supplies and incidentals to complete the work.
1.2 REFERENCES
NOTE: This paragraph is used to list the publications cited in the text of
the guide specification. The publications are referred to in the text by basic
designation only and listed in this paragraph by organization, designation,
date, and title.
Use the Reference Wizard's Check Reference feature when you add a RID outside
of the Section's Reference Article to automatically place the reference in the
Reference Article. Also use the Reference Wizard's Check Reference feature
to update the issue dates.
References not used in the text will automatically be deleted from this section
of the project specification when you choose to reconcile references in the
publish print process.
The publications listed below form a part of this specification to the extent referenced. The publications are
referred to within the text by the basic designation only.
[ASTM INTERNATIONAL (ASTM)ASTM D 4355(2007) Deterioration of Geotextiles from Exposure to Light, Moisture and Heat in a Xenon-Arc Type ApparatusASTM D 4595(2005) Tensile Properties of Geotextiles by the Wide-Width Strip MethodASTM D 4873(2002) Identification, Storage, and Handling of Geosynthetic Rolls and SamplesASTM D 5262(2007) Evaluating the Unconfined Tension Creep Behavior of GeosyntheticsASTM D 5321(2008) Determining the Coefficient of Soil and Geosynthetic or Geosynthetic and Geosynthetic Friction by the Direct Shear MethodASTM D 6637(2001) Standard Test Method for Determining Tensile Properties of Geogrids by the Single or Multi-Rib Tensile MethodASTM D 6706(2001; R 2007) Standard Test Method for Measuring Geosynthetic Pullout Resistance in Soil][GEOSYNTHETIC INSTITUTE (GSI)GSI GRI GG4a(1991) Determination of the Long-Term Design Strength of Stiff GeogridsGSI GRI GG4b(1991) Determination of the Long-Term Design Strength of Flexible GeogridsGSI GRI GG6(1996) Grip Types for Use in Wide Width Testing of Geotextiles and Geogrids]1.3 SUBMITTALS
NOTE: Review submittal description (SD) definitions in Section 01 33 00 SUBMITTAL
PROCEDURES and edit the following list to reflect only the submittals required
for the project. Submittals should be kept to the minimum required for adequate
quality control.
A “G” following a submittal item indicates that the submittal requires Government
approval. Some submittals are already marked with a “G”. Only delete an existing
“G” if the submittal item is not complex and can be reviewed through the Contractor’s
Quality Control system. Only add a “G” if the submittal is sufficiently important
or complex in context of the project.
For submittals requiring Government approval on Army projects, a code of up
to three characters within the submittal tags may be used following the "G"
designation to indicate the approving authority. Codes for Army projects using
the Resident Management System (RMS) are: "AE" for Architect-Engineer; "DO"
for District Office (Engineering Division or other organization in the District
Office); "AO" for Area Office; "RO" for Resident Office; and "PO" for Project
Office. Codes following the "G" typically are not used for Navy, Air Force,
and NASA projects.
Choose the first bracketed item for Navy, Air Force and NASA projects, or choose
the second bracketed item for Army projects.
Government approval is required for submittals with a "G" designation; submittals not having a "G" designation
are for [Contractor Quality Control approval.] [information only. When used, a designation following the "G"
designation identifies the office that will review the submittal for the Government.] Submit the following in
accordance with Section 01 33 00 SUBMITTAL PROCEDURES:
SD-02 Shop Drawings
Installation[; G][; G, [_____]]
Geogrid layout plan along with anchorage and joint details. Sequencing and construction procedures.
Proposed geogrid layout a minimum of 7 days prior to geogrid placement.
SD-03 Product Data
Allowable Strength
Geogrid allowable strength calculated in accordance with GSI GRI GG4a or GSI GRI GG4b. The
calculations shall itemize each reduction factor. Account for splice efficiency in the calculations.
Provide calculations a minimum of 7 days prior to delivery of geogrid to the site.
Manufacturer
Summary of manufacturer's qualifications a minimum of 7 days prior to delivery of geogrid
to the site. Manufacturer's quality control (QC) manual a minimum of 7 days prior to the delivery
of geogrid to the site.
SD-04 Samples
Geogrid Reinforcement
NOTE: The geogrid sample is intended to be for visual demonstration prior to
product delivery. Conformance testing samples, if required, should be obtained
from material actually delivered to the job. If testing is to be performed
for pre qualification, the minimum sample size should be 1 meter (36 inches)
in length and the full roll width. Although 1 square meter (yard) will provide
enough material for testing, the full roll width should be sampled since it
provides a better selection of specimen locations, it clearly shows the machine
and cross directions, and the difference in waste and shipping costs is negligible.
One properly identified 600 by 600 mm 24 by 24 inches minimum size geogrid sample with the fasteners proposed
for use.
SD-06 Test Reports
Geogrid Reinforcement
Manufacturer's certified raw and roll material test reports including ultimate strength performed
in accordance with ASTM D 6637 or ASTM D 4595 (modified). Test results not meeting the requirements
in Table 1 or in the approved Manufacturer's Quality Control Manual will result in rejection
of applicable rolls. Provide certified test reports a minimum of 7 days prior to delivery of
geogrid to the site.
Coefficient of Interaction
The coefficient of interaction for pull-out resistance of the proposed geogrid in a soil of
similar gradation and texture to the material that will be used for fill in the reinforced zone.
Establish the coefficient of interaction in accordance with ASTM D 6706. Provide certified
test results a minimum of 7 days prior to delivery of geogrid to the site.
Interface Friction Testing
Certified laboratory interface friction test results including description of equipment and
test method, a minimum of 7 days prior to delivery of geogrid to the site.
Splices
Test data showing splice efficiency. Provide certified test results a minimum of 7 days prior
to delivery of geogrid to the site.
Conformance Testing
Results of conformance testing.
SD-07 Certificates
Certificates of Compliance
An affidavit certifying raw and roll material test results submitted are accurate and that
the reinforcement meets the requirements of the project specifications. The affidavit shall
be signed by an official authorized to certify on behalf of the manufacturer. [If the affidavit
is dated after award of the contract and/or is not specific to the project, the supplier shall
attach a statement certifying that the affidavit addressed to the wholesale company is representative
of the material supplied.] The documents shall include a statement confirming that all purchased
resin used to produce reinforcement is virgin resin. Provide affidavit a minimum of 7 days
prior to delivery of geogrid to the site.
1.4 QUALITY ASSURANCE
Submit a summary of the manufacturer's qualifications and [_____] copies of the manufacturer's quality control
manual, as specified in the Submittals paragraph. The reinforcement manufacturer shall provide a qualified and
experienced representative to be available on an as-needed basis during construction. The representative shall
visit the site for consultation [at least once during construction] [as requested by the Contracting Officer].
1.5 DELIVERY, STORAGE, AND HANDLING
Check products upon delivery to ensure that the proper material has been received and is dry and undamaged.
Protect the materials from damage and exposure following the guidelines presented in ASTM D 4873.
1.5.1 Labeling
Label each roll with the manufacturer's name, product identification, roll dimensions, lot number, and date manufactured.
1.5.2 Handling
Handle and unload geogrid rolls by hand, or with load carrying straps, a fork lift with a stinger bar, or an
axial bar assembly. Geosynthetic rolls shall not be dragged, lifted by one end, lifted by cables or chains,
or dropped to the ground.
1.5.3 Storage
Protect geogrid from deleterious materials, chemicals, sparks and flames, temperatures in excess of 70 degrees
C 160 degrees F, and any other environmental condition that may degrade the physical properties. If stored outdoors,
the rolls shall be elevated from the ground surface. Protect geogrids, except for extruded grids, with an opaque
waterproof cover.
PART 2 PRODUCTS
2.1 GEOGRID REINFORCEMENT
NOTE: Polyester is susceptible to hydrolysis in alkaline conditions. A high
molecular weight and low carboxyl end group number limit the hydrolysis. Normally,
a mill certificate or certification of these properties is adequate. The molecular
weight of polyester geosynthetics is determined from GSI GRI GG6, "Determination
of the Number Average Molecular Weight of Polyethylene Terephthalate (PET) yarns
Based on a Relative Viscosity Value", and ASTM D 4603, "Determining Inherent
Viscosity of Poly (Ethylene Terephthalate) (PET) by Glass Capillary Viscometer."
The carboxyl end group number is determined from GSI GRI GG7, "Carboxyl End
Group Content of Polyethylene Terephthalate (PET) Yarns."
Provide a geogrid that is a geosynthetic manufactured for reinforcement applications and a regular network of
integrally connected polymer tensile elements with aperture geometry sufficient to permit significant mechanical
interlock with the surrounding soil, aggregate, or other fill materials. The geogrid structure shall be dimensionally
stable and able to retain its geometry under manufacture, transport and installation. The geogrid shall be manufactured
with 100 percent virgin resin consisting of polyethylene, polypropylene, polyester, or other approved material
and with a maximum of 5 percent in-plant regrind material. Polyester resin shall have a minimum molecular weight
of 25,000 and a carboxyl end group number less than 30. Polyethylene and polypropylene shall be stabilized with
long term antioxidants. Submit Certificates of Compliance for the materials provided as specified in the Submittals
paragraph.
2.1.1 Geogrid Reinforcement Properties
The reinforcement shown on the contract drawings shall meet the property requirements listed in Table 1. Reinforcement
strength requirements represent minimum average roll values in the machine direction.
TABLE 1
PROPERTY REQUIREMENT TEST DESIGNATION
Allowable Strength (Ta) [_____] kN/m lb/inch GSI GRI GG4a
at [5] [10] percent or GSI GRI GG4b
strain
UV Resistance 70 percent after ASTM D 4355
500 hours
Coefficient of Interaction
for Pullout [0.85] ASTM D 6706
Interface Friction at [_____] ASTM D 5321
[Peak] [Residual], Degrees
2.1.1.1 Allowable Strength
Allowable Strength is based on reduction factors for installation damage, durability, and creep that are applicable
to site specific conditions. Determine reduction factors in accordance with the test procedures documented in
GSI GRI GG4a or GSI GRI GG4b. The minimum reduction factor for durability shall be 1.1 for polyethylene and
polypropylene geogrids and 1.15 for coated polyester geogrids. The minimum reduction factor for installation
damage shall be 1.1 for all polymers. The reduction factor for creep shall be based on testing performed in
accordance with ASTM D 5262 at the strain specified in Table 1.
2.1.1.2 Interface Friction Testing
NOTE: If the geogrid will not be placed in an anchor trench, interface friction
testing should be conducted to determine the runout length for the geogrid.
All potential slip interfaces beneath the geogrid need to be tested in computing
the required runout length. Normal stresses specified should be representative
of anticipated field conditions. Selection of peak versus residual values should
be based on anticipated interface displacements.
Conduct laboratory interface friction tests on the following interfaces: [_____]. The frequency of testing
for each interface shall be at a rate of [1] [_____] per project. Conduct tests in accordance with ASTM D 5321
. Use normal stresses of [_____], [_____], and [_____] kPa [_____], [_____], and [_____] psi along with a displacement
rate of [5.0] [_____] mm [0.2] [_____] inches per minute. Orient geosynthetics such that the shear force is
parallel to the down slope orientation of these components in the field.
2.2 SPLICES
Splices shall consist of a standard method or device recommended by the manufacturer of the geogrid. Splices
will not be allowed unless identified on the approved layout drawings. Splices shall be at least 75 percent
efficient. Demonstrate the splice efficiency through tests performed in accordance with GSI GRI GG4a or GSI GRI GG4b
. Splicing may consist of overlaps, fusion wedge welding, sewing, or bodkin connections. Splicing methods that
are dependent on installer experience and skill level, such as hot air and torch-applied open flame, are not
acceptable. Construct overlap splices by placing a minimum of 50 mm 2 inches of soil between the layers of geogrid.
PART 3 EXECUTION
3.1 INSTALLATION
3.1.1 Subgrade Preparation
NOTE: For landfill slope reinforcement applications, geogrids are typically
placed directly on the underlying geosynthetic surface.
Immediately prior to placement of the geogrid, the surface on which the geogrid will be placed shall be free
of rock and other material that could damage the geogrid or the underlying geosynthetics.
3.1.2 Anchor Trench
NOTE: Delete this paragraph if an anchor trench is not required. Anchor trench
dimensions need to be determined on a site specific basis.
Anchor trench dimensions must be computed based on the pull-out resistance of
the geogrid. However, pull-out resistance tests (ASTM D 6706) are typically
not performed due to the cost and complexity of this test procedure. Data bases
of interaction coefficients for different geogrids, soils, and loading conditions
are kept by geogrid manufacturers. Information from these data bases should
be used to design the anchorage system.
Place the anchor trench a minimum of [610] [_____] mm [24] [_____] inches back from the edge of the slope to
be covered. The anchor trench shall be a minimum of [610] [_____] mm [24] [_____] inches deep and [610] [_____]
mm [24] [_____] inches wide. Remove ponded water from the anchor trench while the trench is open. Trench corners
shall be rounded to avoid sharp bends in the geogrid. Remove loose soil, rocks larger than [51] [_____] mm [2]
[_____] inches in diameter, and any other material which could reduce the effectiveness of the geogrid from the
surfaces of the trench. Extend the geogrid down the front wall and across the bottom of the anchor trench.
Perform backfilling and compaction of the anchor trench in accordance with Section 31 00 00 EARTHWORK.
3.1.3 Placement
Install the geogrid in accordance with the Manufacturer's recommendations. Unroll the geogrid in the direction
of reinforcement. After a layer of geogrid has been placed, use suitable means, that do not damage the underlying
geosynthetics, to hold the geogrid flat and in place until cover soil can be placed. Geogrid damaged during
placement and covering shall be removed and replaced at no additional cost to the Government.
3.1.4 Overlaps and Fasteners
NOTE: Adjacent rolls of uniaxial geogrid should not be overlapped. The plastic-to-plastic
contact has reduced frictional resistance.
Adjacent rolls of geogrid shall be positioned edge-to-edge and loosely fastened to maintain alignment during
fill placement. Adjacent rolls shall not be overlapped. Use fastener type and spacing as recommended by the
manufacturer and approved by the Contracting Officer. Metallic fasteners will not be allowed.
3.1.5 Splices
Locate splices, if allowed, within the bottom one-third of the slope. Limit splicing to only one splice per
reinforcing strip and no two consecutive reinforcing strips shall include a splice. Individual reinforcing lengths
less than 3 meters 10 feet shall not be used. Splices in geogrid reinforcement shall be pulled and held taut
during cover soil placement.
3.1.6 Penetrations
For small penetrations through geogrids, only transverse members of the geogrid shall be cut. The load-carrying
longitudinal (machine direction) members shall be spread around the penetration. For larger penetrations, additional
geogrid shall be placed on each side of the penetration and spliced to the adjacent geogrid to compensate for
any longitudinal tensile members that must be cut.
3.2 COVER SOIL PLACEMENT
NOTE: The maximum acceptable particle size of cover soil is a function of the
minimum aperture size of the geogrid and the acceptable maximum particle size
against the underlying geosynthetic layer. The book titled "Designing with
Geosynthetics" by Dr. Robert Koerner provides guidance on computing the acceptable
maximum particle size of cover soil material based on the apperature size of
the geogrid.
Cover geogrid with soil within [5] [_____] calendar days of acceptance. Keep the geogrid smooth and taut during
placement of cover materials. Cover soil shall not be dropped onto the geogrid from a height greater than 1
m 3 feet. The soil shall be pushed out over the geogrid in an upward tumbling motion. Place soil from the bottom
of the slope upward. The initial loose soil lift thickness shall be [350] [_____] mm [12] [_____] inches. Use
equipment with ground pressures less than 50 kPa 7 psi to place the first lift over the geogrid. A minimum of
[460] [610] [915] [_____] mm [18] [24] [36] [_____] inches of soil shall be maintained between construction
equipment with ground pressures greater than 50 kPa 7 psi and the geogrid. Equipment placing cover soil shall
not stop abruptly, make sharp turns, spin their wheels, or travel at speeds exceeding [2.2] [_____] m/s [5] [_____]
mph. Additional cover soil material and placement requirements are described in Section 31 00 00 EARTHWORK.
3.3 OVERSIGHT
Keep a QA Representative present at all times during geogrid installation.
3.4 CONFORMANCE TESTING
NOTE: Conformance testing is performed to verify quality control test results
submitted by the manufacturer, to detect degradation during shipping and storage,
and to verify the correct product is supplied. Verification of quality control
by the manufacturer and detecting degradation during shipping and storage is
not economically justified for small jobs. Unlike reinforcing steel for concrete,
geosynthetics are difficult to identify in the field, and even experienced personnel
can sometimes mistake the product identity of unlabeled material. Testing after
delivery to verify the correct product was supplied may be advisable for critical
structures. The strength is usually the most critical property to verify.
Conformance testing expenses are the responsibility of the Contractor. Perform testing using a commercial testing
laboratory selected by the Contractor and approved by the Contracting Officer. The laboratory shall be accredited
via the Geosynthetic Accreditation Institute's Laboratory Accreditation Program (GAI-LAP) for the tests the laboratory
will be required to perform. The Contracting Officer reserves the right to direct the location and select the
material for samples. Conformance test results shall equal or exceed results reported on the Manufacturer's
certified roll material test reports.
TABLE 5. CONFORMANCE TESTING
PROPERTY TEST DESIGNATION FREQUENCY
Wide Width Strip [ASTM D 4595 (mod)] [_____]
Tensile Strength [or] [ASTM D 6637]
Modify ASTM D 4595 for geogrids considering recommendations in GSI GRI GG6. Express the tensile strength on
a unit length basis by substituting n*a for Ws, where:
Ws = specimen width, (mm inches)
n = number of ribs in the sample (must be a whole number)
a = nominal rib spacing for the product tested, (mm inches)